This invention relates to flashing advisory signs of the type frequently found in a vehicular traffic environment.
Advisory signs are widely used on highways to provide a variety of messages to motorists, such as intersection control information, highway condition information (both permanent and temporary) and traffic control information. The use of such signs has become so uniform that sign standards have been established for color, shape and size of such signs. These signs may be generally classified as stationary, temporary and moveable. Examples of stationary or fixed signs are such intersection control signs as STOP, DO NOT ENTER, and NO LEFT TURN, and advisory signs such as SCHOOL XING and FREEWAY ENTRANCE: these signs are typically affixed to a stanchion or post permanently anchored at the traffic intersection control or advisory site. Examples of temporary signs are signs such as MEN WORKING and DETOUR: these signs are usually temporarily installed at a work site on tripods or other suitable sign mounting devices and later removed. An example of a moveable sign is the sequentially operated directional arrow signs found on the back of transportation authority trucks or on trailers left at a construction site.
Traffic advisory signs commonly employ a reflective color background and message portion (the latter in words or symbols or a combination of both) adhered to a relatively stiff backing member, typically fabricated from metal. Some signs include the addition of one or more flashing illumination lamps in order to draw the attention of motorists to the advisory sign. Still other signs are entirely constructed from individual lamps arranged to form the message information, such as the arrowheads noted above.
Nonilluminated signs (i.e., standard signs with no flashing illumination lamp) have a lower threshold of noticeability than signs provided with flashing illumination lamps or signs made from individual lamps forming the message when flashed. Nevertheless, the vast majority of advisory signs do not employ flashing illumination lamps, primarily for two reasons. Firstly, both the initial installation costs and the operating costs of signs employing flashing lamps is substantially higher than an ordinary sign, due to the necessity for a power connection to a flashing lamp sign, the increased maintenance required by lamp failures (either naturally or through vandalism), and the relatively high power consumption of AC operated lamps. With respect to the matter of cost, it is noted that flashing moveable signs (like those mounted on the rear of a truck or trailer) require a separate electrical power source, usually in the form of a diesel powered electrical generator, to operate the electrical lamps. Such independent power sources require periodic maintenance, are prone to theft and represent a relatively high capital investment per unit. Secondly, some signs are located in residential areas (such as DEAD END and STOP signs) and the repetitive flashing of the lamps throughout the night is annoying to those residing in the vicinity. Thus, even though signs provided with flashing illumination lamps are more desirable from a traffic safety standpoint, the deployment of such signs has been limited in the past.
Standard signs also suffer from the disadvantage that exposure to sunlight, rain, snow, mud and other environmental contaminants deteriorates the reflective substances forming the sign message. As a consequence, standard signs have an average useful lifetime in situ which is much shorter than the potential lifetime absent such exposure.
Flashing signs suffer from the disadvantage of being difficult to read or unnoticeable when exposed to direct unlight. In addition, the functional efficiency of such signs is relatively low. Specifically, that portion of a flashing sign which provides the visual stimulation to the motorist is the light bulb. For a typical single lamp flashing sign, the bulb has circular projected area of about one-third square foot (for a bulb with a diameter of about eight inches) while the sign itself has an area of at least nine square feet. For a typical arrowhead sign, each sign typically employs fifteen bulbs with a total projected area of about five and one-quarter square feet in a housing of eighteen square feet in area. In either case, the ratio of the bulb area to the sign area is relatively small.